Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry. The processing circuitry can receive coded information of pictures in a coded video sequence. The coded information can include a coding tree unit (CTU) size information that indicates a CTU size selected for the pictures. The CTU size information can be encoded using a truncated unary code. The processing circuitry can determine the selected CTU size based on the CTU size information encoded using the truncated unary code. The processing circuitry can reconstruct samples in the pictures based on the selected CTU size. The selected CTU size can be 32×32, 64×64, or 128×128 luma samples.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/886,056, “Improved SPS Header Syntax andDescriptor for CTU Size” filed on Aug. 13, 2019, which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine differentdirections could be represented. That increased to 33 in H.265 (year2013), and JEM/VVC/BMS, at the time of disclosure, can support up to 65directions. Experiments have been conducted to identify the most likelydirections, and certain techniques in the entropy coding are used torepresent those likely directions in a small number of bits, accepting acertain penalty for less likely directions. Further, the directionsthemselves can sometimes be predicted from neighboring directions usedin neighboring, already decoded, blocks.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry can receivecoded information of pictures in a coded video sequence. The codedinformation can include a coding tree unit (CTU) size information thatindicates a CTU size selected for the pictures. The CTU size informationcan be encoded using a truncated unary code. The processing circuitrycan determine the selected CTU size based on the CTU size informationencoded using the truncated unary code and reconstruct samples in thepictures based on the selected CTU size. In an embodiment, the selectedCTU size is 32×32, 64×64, or 128×128 luma samples.

In an embodiment, the processing circuitry can determine, based on theCTU size information encoded using the truncated unary code, a codedvalue from a bit string in the coded information where a maximum numberof bits in the bit string is 2. The coded value can be 0, 1, and 2 whenthe bit string is 0, 10, and 11, respectively. The processing circuitrycan determine the selected CTU size based on the coded value.

In an example, the processing circuitry can determine that the selectedCTU size is 128, 64, and 32 in a case that the coded value is 0, 1, and2, respectively. The processing circuitry can determine the selected CTUsize to be 2^(CtbLog2SizeY) where a value of CtbLog 2SizeY is adifference between 7 and the coded value.

In an example, the processing circuitry can determine that the selectedCTU size is 32, 64, and 128 in a case that the coded value is 0, 1, and2, respectively. The processing circuitry can determine the selected CTUsize to be 2^(CtbLog2SizeY) where a value of CtbLog 2SizeY is a sum ofthe coded value and 5.

In an embodiment, the coded information is in a sequence parameter setheader for the coded video sequence.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform any of themethods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIGS. 9A-9B show a coding tree unit (CTU) and a quadtree plus binarytree (QTBT) structure according to embodiments of the disclosure.

FIG. 10A shows an example of a syntax and a corresponding descriptor inan Sequence Parameter Setting (SPS) header according to an embodiment ofthe disclosure.

FIG. 10B shows an example of unsigned integer Exp-Golomb codingaccording to an embodiment of the disclosure.

FIG. 11A shows an example of a syntax and a corresponding descriptor inan SPS header according to an embodiment of the disclosure.

FIG. 11B shows an example of a fixed-length coding using 2 bitsaccording to an embodiment of the disclosure.

FIG. 12A shows an example of a syntax and a corresponding descriptor inan SPS header according to an embodiment of the disclosure.

FIG. 12B shows an example of truncated unary coding according to anembodiment of the disclosure.

FIG. 13 shows a flow chart outlining a process (1300) according to anembodiment of the disclosure.

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

A block partitioning structure can be referred to as a coding tree. Insome embodiments, the block partitioning structure uses a quad-tree (QT)plus binary tree (BT). For example, by using a QT structure, a CTU issplit into CUs to adapt to various local characteristics. A decision onwhether to code a picture area using an inter-picture (temporal) orintra-picture (spatial) prediction can be made at a CU level. Each CUcan be further split into one, two, or four PUs according to a PUsplitting type. Inside one PU, a same prediction process is applied andrelevant information can be transmitted to a decoder on a PU basis.

After obtaining a residual block by applying a prediction process basedon the PU splitting type, a CU can be partitioned into TUs according toanother QT structure. As can be seen, there are multiple partitionconceptions including CU, PU, and TU.

At a picture boundary, in some embodiments, implicit quadtree split canbe employed so that a block will keep QT splitting until the size fitsthe picture boundary.

In some embodiments, a quadtree plus binary tree (QTBT) structure isemployed. The QTBT structure removes the concepts of multiple partitiontypes (e.g., the CU, PU, and TU concepts), and supports more flexibilityfor CU partition shapes. In the QTBT block structure, a CU can haveeither a square or rectangular shape.

FIG. 9A shows a CTU (910) that is partitioned by using a QTBT structure(920) shown in FIG. 9B. The CTU (910) is first partitioned by a QTstructure. The QT leaf nodes are further partitioned by a BT structureor a QT structure. There can be two splitting types, symmetrichorizontal splitting and symmetric vertical splitting, in the BTsplitting. The BT leaf nodes are called CUs that can be used forprediction and transform processing without any further partitioning.Accordingly, CU, PU, and TU have the same block size in the QTBT codingblock structure.

In some embodiments, a CU can include coding blocks (CBs) of differentcolor components. For example, one CU contains one luma CB and twochroma CBs in the case of P and B slices of the 4:2:0 chroma format. ACU can include a CB of a single color component. For example, one CUcontains only one luma CB or just two chroma CBs in the case of Islices.

The following parameters are defined for the QTBT partitioning scheme insome embodiments:

-   -   CTU size: root node size of a quadtree, e.g., such as in HEVC.    -   MinQTSize: minimum allowed QT leaf node size.    -   MaxBTSize: maximum allowed BT root node size.    -   MaxBTDepth: maximum allowed BT depth.    -   MinBTSize: minimum allowed BT leaf node size.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The QT partitioning is applied to the CTU firstto generate QT leaf nodes. The QT leaf nodes may have a size from 16×16(i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If the leaf QTnode is 128×128, it will not be further split by the binary tree sincethe size exceeds the MaxBTSize (i.e., 64×64). Otherwise, the leaf QTnode could be further partitioned by the binary tree. Therefore, the QTleaf node is also the root node for the binary tree and it has the BTdepth as 0.

When the BT depth reaches MaxBTDepth (i.e., 4), no further splitting isconsidered. When the BT node has a width equal to MinBTSize (i.e., 4),no further horizontal splitting is considered. Similarly, when the BTnode has height equal to MinBTSize, no further vertical splitting isconsidered. The leaf nodes of the binary tree are further processed byprediction and transform processing without any further partitioning. Inan embodiment, a maximum CTU size is 256×256 luma samples.

In FIGS. 9A and 9B, the solid lines indicate QT splitting and dottedlines indicate BT splitting. In each splitting (i.e., non-leaf) node ofthe binary tree, one flag can be signaled to indicate which splittingtype (i.e., horizontal or vertical) is used. For example, 0 indicates ahorizontal splitting and 1 indicates a vertical splitting. For the QTsplitting, there is no need to indicate the splitting type sincequadtree splitting always splits a block both horizontally andvertically to produce 4 sub-blocks with an equal size.

In some embodiments, the QTBT scheme supports the flexibility for theluma and chroma to have a separate QTBT structure. For example, for Pand B slices, the luma and chroma blocks in one CTU share the same QTBTstructure. However, for I slices, the luma CTB is partitioned into CUsby a QTBT structure, and the chroma blocks are partitioned into chromaCUs by another QTBT structure. Thus, a CU in an I slice can include, orconsist of, a coding block of the luma component or coding blocks of twochroma components, and a CU in a P or B slice can include, or consistof, coding blocks of all three color components.

In some embodiments, inter prediction for small blocks is restricted toreduce memory access of motion compensation. For example, bi-predictionis not supported for 4×8 and 8×4 blocks, and inter prediction is notsupported for 4×4 blocks. In some examples, such as when the QTBT isimplemented, the above restrictions can be removed.

A CTU size can be represented by a width (or a height) M of a CTU. In anembodiment, when the CTU has a square shape, the CTU size can also berepresented by M×M luma samples in the CTU. Thus, the CTU size can bereferred to as M or M×M. In an embodiment, a same CTU size can be usedto code (e.g., encode/decode) pictures in a video sequence, and codinginformation indicating the CTU size can be signaled in a SequenceParameter Setting (SPS) (e.g., in a SPS header) and shared among thepictures in the video sequence.

In some embodiments, a plurality of CTU sizes (e.g., four CTU sizes),such as 16, 32, 64, and 128, can be used. Thus, the four CTU sizes canbe 16×16, 32×32, 64×64, and 128×128 luma samples, respectively. Avarible ‘CtbSizeY’ can be used to represent the four CTU sizes (e.g.,16, 32, 64, and 128). Numbers 4-7 are the base 2 logarithms of the fourCTU sizes 16, 32, 64, and 128, respectively, and can be represented by avariable ‘CtbLog 2SizeY’. Four numbers 2, 3, 4, and 5 can be used tocode 16 (or 16×16 luma samples), 32 (or 32×32 luma samples), 64 (or64×64 luma samples), and 128 (or 128×128 luma samples), respectively,and can be represented by a variable ‘log 2_ctu_size_minus2’. Forexample, the four numbers 2-5 (or log 2_ctu_size_minus2) are differencesbetween the base 2 logarithms (or CtbLog 2SizeY) of the four CTU sizes16, 32, 64, and 128 and a value 2, respectively. An example of a SPSheader syntax for CTU sizes can be set to ‘log 2_ctu_size_minus2’ asshown in FIG. 10A.

The four numbers 2-5 (or log 2_ctu_size_minus2) can be coded using anentropy coding tool, for example Exp-Golomb coding, such as unsignedinteger 0-th order Exp-Golomb coding (or ue(v)). Thus, a correspondingdescriptor for the variable log 2_ctu_size_minus2 is ue(v) in FIG. 10A.

FIG. 10B shows an example of ue(v) coding according to an embodiment ofthe disclosure. Variable bit strings (1010) can be used to code thevariable log 2_ctu_size_minus2 (also referred to coded values or codenumbers (codeNums)) (1020). For example, the bit strings 011, 00100,00101, and 00110 are used to code the codeNums 2-5, respectively.

Based on the description above, semantics for CTU sizes can be describedbelow. log 2_ctu_size_minus2 plus 2 specifies a luma CTB size of eachCTU (as shown in Eq. (1)). log 2_min_luma_coding_block_size_minus2 plus2 specifies a minimum luma coding block size.

The variables CtbLog 2SizeY and CtbSizeY can be derived using Eqs.(1)-(2).Ctb Log 2SizeY=log 2_ctu_size_minus2+2  Eq. (1)CtbSizeY=1<<Ctb Log 2SizeY  Eq. (2)

For example, the bit string 011 represents the codeNum 2 based on ue(v)coding as shown in FIG. 10B. Thus, a value of the variable log2_ctu_size_minus2 is 2. A value of the variable CtbLog 2SizeY isdetermined to be 4 based on Eq. (1). A value of the variable CtbSizeY isdetermined to be 2^(CtbLog2SizeY) based on Eq. (2), and thus the valueof the variable CtbSizeY is 2⁴=16. Thus, the CTU size is 16 or 16×16luma samples. The above description can be applied to other bit stringsthat indicate various CTU sizes, such as 32, 64, or 128.

In some examples, a much larger overhead can occur when using the CTUsize 16 instead of using larger CTU sizes (e.g., 128). Thus, a decodingtime can be longer when using the CTU size 16. In an example, a CTU sizeof 16×16 luma samples corresponds to an 8×8 chroma CTB size. For certaincoding modules, processing the 8×8 chroma CTB size is challengingbecause a loop filter typically uses a 16×16 block as an input. Further,the CTU size 16×16 can cause a significant encoding loss. Thus, the CTUsize 16 can be removed.

In some embodiments, a plurality of CTU sizes (e.g., three CTU sizes),such as 32, 64, and 128 (or 32×32, 64×64, 128×128 luma samples) areused. Similarly, the varible ‘CtbSizeY’ can be used to represent thethree CTU sizes. Numbers 5-7 are the base 2 logarithms of the three CTUsizes 32, 64, and 128, respectively, and can be represented by thevariable ‘CtbLog 2SizeY’. Syntax and corresponding description in theSPE header can be modified as below and shown in FIG. 11A.

Three numbers 0-2 can be used to code the three CTU sizes, e.g., 32 (or32×32 luma samples), 64 (or 64×64 luma samples), and 128 (or 128×128luma samples), respectively, and can be represented by a variable ‘log2_ctu_size_minus5’. For example, the three numbers 0-2 (or log2_ctu_size_minus5) are differences between the base 2 logarithms (i.e.,5-7) (or CtbLog 2SizeY) of the three CTU sizes 32, 64, and 128 and anumber 5, respectively. As described above, a SPS header syntax for CTUsizes can be set to log 2_ctu_size_minus5′ as shown in FIG. 11A.

The three numbers 0-2 (or log 2_ctu_size_minus5) can be coded using anentropy coding tool having a fixed length coding, such as unsignedinteger using n bits (or u(n)). In an example, 2 bits can be used (e.g.,n=2). Thus, a corresponding descriptor is u(2) in FIG. 11A. ComparingFIGS. 10A and 11A, the differences are indicated by labels 1110 and1120.

FIG. 11B shows an example of u(2) coding according to an embodiment ofthe disclosure. Fixed-length bit strings (1130) can be used to code thevariable log 2_ctu_size_minus5 (also referred to coded values orcodeNums) (1140). For example, the bit strings 00, 01, and 10 can beused to code the codeNums 0-2, respectively.

Semantics for CTU sizes are described as follows, and some differencesassociated with log 2_ctu_size_minus2 and log 2_ctu_size_minus5 arehighlighted using italics.

log 2_ctu_size_minus5 plus 5 specifies the luma CTB size of each CTU. Inan example, it is a requirement of bitstream conformance that the valueof log 2_ctu_size_minus5 be less than or equal to 2.

log 2_min_luma_coding_block_size_minus2 plus 2 can specify the minimumluma coding block size.

The variables CtbLog 2SizeY and CtbSizeY can be derived using Eqs.(2)-(3) where Eq. (3) is different from Eq. (1).Ctb Log 2SizeY=log 2_ctu_size_minus5+5  Eq. (3)

For example, the bit string 00 represents the codeNum 0 based on u(2)coding as shown in FIG. 11B. Thus, log 2_ctu_size_minus5 is 0. A valueof the variable CtbLog 2SizeY is determined to be 5 based on Eq. (3). Avalue of the variable CtbSizeY is determined to be 2^(CtbLog2SizeY)based on Eq. (2), and thus the value of the variable CtbSizeY is 2⁵=32.Thus, the CTU size is 32 or 32×32 luma samples. The above descriptioncan be applied to other bit strings that indicates other CTU sizes(e.g., 64 or 128).

In some embodiments, only three numbers (e.g., the codeNums 0-2)representing the three CTU sizes are encoded. Using the fixed lengthcoding u(2) to describe the syntax log 2_ctu_size_minus5 can waste onebit, for example, when the encoded number is 0 or 1.

In some embodiments described above, the number 0 (e.g., the codeNum 0)can be used to represent the CTU size 32 (or 32×32 luma samples) and thenumber 2 (e.g., the codeNum 2) can be used to represent the CTU size 128(or 128×128 luma samples). In various examples, the CTU size 128 is themost frequently used CTU size in a video sequence, and thus encoding theCTU size 128 with the number 2 can decrease coding efficiency andincrease coding complexity.

In some embodiments, for pictures in a video sequence, a CTU size to beused for coding the pictures can be indicated in coded information forthe video sequence. Information indicating the CTU size can be in an SPSheader. The CTU size can be one of a plurality of CTU sizes, such as thethree CTU sizes 32, 64, and 128. According to aspects of the disclosure,a truncated unary coding can be used to code (e.g., encode/decode)numbers (e.g., coded values or codeNums) indicating CTU sizes. Whencompared with the fixed-length coding described in above (e.g., withreference to FIGS. 11A-11B), the truncated unary coding can improvecoding efficiency, for example, by eliminating unnecessary waste ofbits. Thus, a size of the SPS header can be smaller when the truncatedunary coding is used instead of the fixed-length coding u(2), and thusimproving the coding efficiency. Further, in some examples, an illegalbitstream generated by a non-conforming encoder (e.g., enabling the CTUsize 16×16 that is not allowed in some standards or coders) can beavoided.

In an embodiment, the three CTU sizes 32, 64, and 128 (or 32×32, 64×64,128×128 luma samples) can be used. As described above, the variable‘CtbSizeY’ can be used to represent the three CTU sizes. Numbers 5-7 arethe base 2 logarithms of the three CTU sizes 32, 64, and 128,respectively, and can be represented by the variable ‘CtbLog 2SizeY’.Syntax and corresponding description in the SPS header can be modifiedas below and shown in FIG. 12A.

The three numbers 0-2 can be used to code or represent the three CTUsizes. According to aspects of the disclosure, 0 is used to represent(or code) 128 (or 128×128 luma samples), 1 is used to represent (orcode) 64 (or 64×64 luma samples), and 2 is used to represent (or code)32 (or 32×32 luma samples), and thus the three numbers can berepresented by a variable ‘seven_minus_log 2_ctu_size’. For example, thethree numbers 0-2 (or seven_minus_log 2_ctu_size) are differencesbetween 7 and the base 2 logarithms 7, 6, and 5 (or CtbLog 2SizeY) ofthe three CTU sizes 128, 64, and 32, respectively. As described above, aSPS header syntax for CTU sizes can be set to ‘seven_minus_log2_ctu_size’ as shown in FIG. 12A.

The three numbers 0-2 (or seven_minus_log 2_ctu_size) can be coded usingthe truncated unary coding (or tu(v)) as shown by a descriptor is tu(v)in FIG. 12A. In an embodiment, the truncated unary coding is a unarycoding that generates a bin string (or bit string) of ‘1’ followed by a‘0’ when a number to be coded is less than a maximum value cMax. Whenthe number to be coded is equal to the maximum value cMax, the last ‘0’is truncated. In an embodiment, the maximum value cMax is 2 when codingthe three numbers 0-2 (or seven_minus_log 2_ctu_size). FIG. 12B shows anexample of the truncated unary coding according to an embodiment of thedisclosure. Variable-length bit strings (1230) are used to code thevariable seven_minus_log 2_ctu_size (also referred to coded values orcodeNums (1240)). The bit string 0 can be used to code the codeNum 0.The bit string 10 can be used to code the codeNum 1. The bit string 11can be used to code the codeNum 2. Comparing FIGS. 11A and 12A, thedifferences are indicated by labels (1210) and (1220). Comparing FIGS.10A and 12A, the differences are indicated by the labels (1210) and(1220).

In general, the three numbers 0-2 (or seven_minus_log 2_ctu_size) can becoded using any suitable coding method, such as variable-length coding(e.g., the truncated unary coding, Exp-Golomb coding), fixed-lengthcoding (e.g., u(n)), or the like where the number 0 represents the CTUsize 128. Code numbers can be assigned based on frequency of use of theCTU size. For example, a CTU size of 128 can be assigned to a lowest orsmaller code number.

As described above in FIGS. 12A-12B, the variable ‘seven_minus_log2_ctu_size’ can be used to describe CTU sizes, and the CTU size 128 canbe coded with the coded value or the codeNum 0. Further, the bit string0 having 1 bit can be used to code the codeNum 0. In various examples,when the CTU size 128 is used more frequently than other CTU sizes(e.g., 32 and 64), coding the CTU size 128 with 1 bit can improve codingefficiency. For example, the bit string 00110 can be used to indicatethe CTU size 128 has 5 bits (FIG. 10B) or the bit string 10 can used toindicate the CTU size 128 has 2 bits (FIG. 11B).

Semantics for CTU sizes are described as follows, and some differencesbetween seven_minus_log 2_ctu_size and other variable(s) (log2_ctu_size_minus5 and log 2_ctu_size_minus2) are highlighted usingitalics.

seven_minus_log 2_ctu_size specifies the luma CTB size of each CTU. Inan example, it is a requirement of bitstream conformance that the valueof seven_minus_log 2_ctu_size be less than or equal to 2.

log 2_min_luma_coding_block_size_minus2 plus 2 can specify the minimumluma coding block size.

The variables CtbLog 2SizeY and CtbSizeY can be derived using Eqs. (2)and (4).Ctb Log 2SizeY=7−seven_minus_log 2_ctu_size  Eq. (4)

Referring to FIG. 12B, for example, the bit string 0 can be used torepresent the codeNum 0 based on tu(v) coding having the maximum valuecMax of 2. Thus, a value of the variable seven_minus_log 2_ctu_size is0. A value of the variable CtbLog 2SizeY is determined to be 7 based onEq. (4). A value of the variable CtbSizeY is determined to be2^(CtbLog2SizeY) based on Eq. (2), and thus the value of the variableCtbSizeY is 2⁷=128. Thus, the CTU size is 128 or 128×128 luma samples.The above description can be applied to other bit strings that indicateother CTU sizes (e.g., 32 or 64).

According to aspects of the disclosure, the coded information of thepictures in the coded video sequence can be received by a decoder. Thecoded information can indicate a CTU size that is selected or used toencode the pictures, for example, by an encoder. The selected CTU sizecan be one of a plurality of CTU sizes, such as the three CTU sizes 32,64, and 128. The coded information can be encoded/decoded using thetruncated unary coding to obtain the selected CTU size. In an example,the coding information can indicate a coding tool (e.g., the truncatedunary coding) used to code the CTU size. In another example, the codingtool is predetermined or signaled beforehand.

In an embodiment, the coded information is in an SPS header (e.g., asyntax and a descriptor of the SPS header), such as described above withreference to FIGS. 12A-12B. The coded information can include a bitstring (e.g., the bit string 10 in FIG. 12B). In an example, a codedvalue/codeNum (e.g., a seven_minus_log 2_ctu_size) can be determinedfrom the bit string using the truncated unary coding and the coded valueis the number 1 shown in FIG. 12B. In an example, the maximum value cMaxused in the truncated unary coding is 2. Further, the selected CTU size(e.g., 64) can be determined from the coded value (e.g., the number 1)based on the syntax and associated semantics (e.g., Eq. (4) and Eq.(2)). For example, a value of the variable CtbLog 2SizeY is determinedto be a difference between 7 and the coded value using Eq. (4), and thusthe value of the variable CtbLog 2SizeY is 7 when seven_minus_log2_ctu_size is 0. Then a value of the variable CtbSizeY is determined tobe 2^(CtbLog2SizeY) using Eq. (2), and thus the value of the variableCtbSizeY is 2⁷=128 when CtbLog 2SizeY is 7.

As described above with reference to FIGS. 12A-12B, coding a mostfrequently used CTU size with a smaller number of bits can improvecoding efficiency. In some examples, the most frequently used CTU sizeis 128, and thus the CTU size 128 can be coded with 1 bit (e.g., the bitstring ‘0’ as shown in FIG. 12B).

In some embodiments, a plurality of CTU sizes (e.g., three CTU sizes),such as 32, 64, and 128, can be represented using the variable log2_ctu_size_minus5, for example, using Eqs. (2) and (3) and coded usingtruncated unary coding tu(v) having the maximum value cMax of 2, such asshown in FIG. 12B. In an example, the CTU size 128 is encoded with thecoded value (or codeNum) 2, and thus the bit string 11 is used to encodethe number 2 and the CTU size 128. In an example the CTU size 64 isencoded with the coded value (or codeNum) 1, and thus the bit string 10is used to encode the number 1 and the CTU size 64. In an example, theCTU size 32 is encoded with the coded value (or codeNum) 0, and thus thebit string 0 is used to encode the number 0 and the CTU size 32. Thus, acoded value (or log 2_ctu_size_minus5) can be determined from a bitstring using the truncated unary coding with the maximum value cMax of2. Further, the selected CTU size can be determined from the coded valuebased on the syntax and associated semantics (e.g., Eq. (3) and Eq.(2)). For example, a value of the variable CtbLog 2SizeY can bedetermined to be a sum of 5 and the coded value using Eq. (3). Then avalue of the variable CtbSizeY can be determined to be 2^(CtbLog2SizeY)using Eq. (2).

FIG. 13 shows a flow chart outlining a process (1300) according to anembodiment of the disclosure. The process (1300) can be used todetermine a CTU size to be used for pictures in a coded video sequence.In various embodiments, the process (1300) are executed by processingcircuitry, such as the processing circuitry in the terminal devices(310), (320), (330) and (340), the processing circuitry that performsfunctions of the video encoder (403), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the video decoder (510), the processingcircuitry that performs functions of the video encoder (603), and thelike. In some embodiments, the process (1300) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1300). Theprocess starts at (S1301) and proceeds to (S1310).

At (S1310), coded information of the pictures in the coded videosequence can be received, for example, by a decoder. The codedinformation can include CTU size information that indicates a CTU sizethat is selected for the pictures, for example, by an encoder to encodethe pictures. The selected CTU size can be one of a plurality of CTUsizes, such as the three CTU sizes 32×32, 64×64, and 128×128 lumasamples. The plurality of CTU sizes can include any suitable number ofCTU sizes and can include any suitable CTU size(s). The CTU sizeinformation can be encoded using the truncated unary code or othercoding schemes.

In an example, the coded information indicates a coding tool used tocode the selected CTU size. For example, the coding information is in anSPS header that indicates the coding tool (e.g., tu(v), u(2), or ue(v)).In some examples, the syntax is included in the SPS header, and thusindicating the corresponding semantics.

At (S1320), the selected CTU size can be determined using the codingtool (e.g., the truncated unary coding) based on the CTU sizeinformation. For example, the coded information is decoded using thetruncated unary decoding, as described above with reference to FIGS.12A-12B. In an embodiment, the CTU size information includes a bitstring. A coded value (e.g., a codeNum) can be determined from the bitstring using the truncated unary decoding. For example, the coded valuecan be determined to be 0, 1, and 2 when the bit string is 0, 10, and11, respectively and a maximum value Cmax used in the truncated unarycoding is 2. Further, the selected CTU size can be determined based onthe coded value, for example, using the syntax (or the correspondingsemantics) indicated in the coding information.

In an example, the syntax indicates that the coded value refers to avalue of the variable seven_minus_log 2_ctu_size, and thus Eqs. (2) and(4) can be used to obtain the CTU size. Accordingly, the selected CTUsize is 128 when the coded value is 0. The selected CTU size is 64 whenthe coded value is 1. The selected CTU size is 32 when the coded valueis 2. Further, the selected CTU size can be determined to be2^(CtbLog2SizeY) where a value of the variable CtbLog 2SizeY is adifference between 7 and the coded value.

In an example, the syntax indicates that the coded value refers to avalue of the variable log 2_ctu_size_minus5, and thus Eqs. (2) and (3)can be used to obtain the selected CTU size. Accordingly, the selectedCTU size is 128 when the coded value is 2. The selected CTU size is 64when the coded value is 1. The selected CTU size is 32 when the codedvalue is 0. Further, the selected CTU size can be determined to be2^(CtbLog2SizeY) where a value of the variable CtbLog 2SizeY is a sum ofthe coded value and 5.

At (S1330), samples in the pictures can be reconstructed based on theselected CTU size. For example, one of the pictures can be partitionedinto CTUs having the selected CTU size. Each of the CTUs can be furtherpartitioned into CUs where inter predictions and/or intra prediction canbe used to reconstruct the samples in the CUs. The process (1300)proceeds to (S1399) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can be also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration model

VVC: versatile video coding

BMS: benchmark set

MV: Motion Vector

HEVC: High Efficiency Video Coding

MPM: most probable mode

WAIP: Wide-Angle Intra Prediction

SEI: Supplementary Enhancement Information

VUI: Video Usability Information

GOPs: Groups of Pictures

TUs: Transform Units,

PUs: Prediction Units

CTUs: Coding Tree Units

CTBs: Coding Tree Blocks

PBs: Prediction Blocks

HRD: Hypothetical Reference Decoder

SDR: standard dynamic range

SNR: Signal Noise Ratio

CPUs: Central Processing Units

GPUs: Graphics Processing Units

CRT: Cathode Ray Tube

LCD: Liquid-Crystal Display

OLED: Organic Light-Emitting Diode

CD: Compact Disc

DVD: Digital Video Disc

ROM: Read-Only Memory

RAM: Random Access Memory

ASIC: Application-Specific Integrated Circuit

PLD: Programmable Logic Device

LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution

CANBus: Controller Area Network Bus

USB: Universal Serial Bus

PCI: Peripheral Component Interconnect

FPGA: Field Programmable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit

CU: Coding Unit

PDPC: Position Dependent Prediction Combination

ISP: Intra Sub-Partitions

SPS: Sequence Parameter Setting

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: receiving coded information of pictures in a coded videosequence, the coded information including a coding tree unit (CTU) sizeinformation that indicates a CTU size selected for the pictures fromthree CTU sizes; determining, based on at least one bit corresponding tothe CTU size information, the selected CTU size; and reconstructingsamples in the pictures based on the selected CTU size, wherein theselected CTU size is determined as a first CTU size of the three CTUsizes based on a first bit of the at least one bit corresponding to theCTU size information being a first value, the selected CTU size isdetermined as one of a second CTU size and a third CTU size of the threeCTU sizes based on the first bit being a second value and a second bitof the at least one bit corresponding to the CTU size information, andthe at least one bit includes the second bit based on the first bitbeing the second value.
 2. The method of claim 1, wherein the three CTUsizes are 32, 64, and 128, and the selected CTU size is 32, 64, or 128indicating each of the pictures has 32×32, 64×64, or 128×128 lumasamples, respectively.
 3. The method of claim 2, wherein the determiningthe selected CTU size comprises: determining, based on the CTU sizeinformation encoded using a truncated unary coding, a coded value fromthe at least one bit in the coded information, a maximum number of bitsin the at least one bit being 2, the coded value being 0 when the atleast one bit is 0, the coded value being 1 when the at least one bit is10, and the coded value being 2 when the at least one bit is
 11. 4. Themethod of claim 3, wherein the determining the selected CTU sizecomprises: determining that the selected CTU size is 128, 64, or 32 in acase that the coded value is 0, 1, or 2, respectively.
 5. The method ofclaim 4, wherein the determining the selected CTU size is 128, 64, or 32comprises: determining, based on the coded value corresponding to theCTU size information, a variable value equal to a difference of thecoded value and a predetermined constant value, the predeterminedconstant value being an odd prime number; and determining the selectedCTU size to be 2^(CtbLog2SizeY), the variable value being CtbLog2SizeY.6. The method of claim 3, wherein the determining the selected CTU sizecomprises: determining, based on the coded value corresponding to theCTU size information, a variable value to be (7—the coded value), anddetermining the selected CTU size to be 2^(CtbLog2SizeY), the variablevalue being CtbLog 2SizeY.
 7. The method of claim 3, wherein thedetermining the selected CTU size comprises: determining a variablevalue to be a sum of the coded value and 5; and determining the selectedCTU size to be 2^(CtbLog2SizeY), the variable value being CtbLog 2SizeY.8. The method of claim 1, wherein the coded information is in a sequenceparameter set header for the coded video sequence.
 9. An apparatus forvideo decoding, comprising: processing circuitry configured to: receivecoded information of pictures in a coded video sequence, the codedinformation including a coding tree unit (CTU) size information thatindicates a CTU size selected for the pictures from three CTU sizes;determine, based on at least one bit corresponding to the CTU sizeinformation, the selected CTU size; and reconstruct samples in thepictures based on the selected CTU size, wherein the selected CTU sizeis determined as a first CTU size of the three CTU sizes based on afirst bit of the at least one bit corresponding to the CTU sizeinformation being a first value, the selected CTU size is determined asone of a second CTU size and a third CTU size of the three CTU sizesbased on the first bit being a second value and a second bit of the atleast one bit corresponding to the CTU size information, and the atleast one bit includes the second bit based on the first bit being thesecond value.
 10. The apparatus of claim 9, wherein the three CTU sizesare 32, 64, and 128, and the selected CTU size is 32, 64, or 128indicating each of the pictures has 32×32, 64×64, or 128×128 lumasamples, respectively.
 11. The apparatus of claim 10, wherein theprocessing circuitry is configured to: determine, based on the CTU sizeinformation encoded using a truncated unary coding, a coded value fromthe at least one bit in the coded information, a maximum number of bitsin the at least one bit being 2, the coded value being 0 when the atleast one bit is 0, the coded value being 1 when the at least one bit is10, and the coded value being 2 when the at least one bit is
 11. 12. Theapparatus of claim 11, wherein the processing circuitry is configuredto: determine that the selected CTU size is 128, 64, or 32 in a casethat the coded value is 0, 1, or 2, respectively.
 13. The apparatus ofclaim 12, wherein the processing circuitry is configured to: determine,based on the coded value corresponding to the CTU size information, avariable value equal to a difference of the coded value and apredetermined constant value, the predetermined constant value being anodd prime number; and determine the selected CTU size to be2^(CtbLog2SizeY), the variable value being CtbLog 2SizeY.
 14. Theapparatus of claim 11, wherein the processing circuitry is configuredto: determine, based on the coded value corresponding to the CTU sizeinformation, a variable value to be (7—the coded value), and determinethe selected CTU size to be 2^(CtbLog2SizeY), the variable value beingCtbLog 2SizeY.
 15. The apparatus of claim 11, wherein the processingcircuitry is configured to: determine a variable value to be a sum ofthe coded value and 5; and determine the selected CTU size to be2^(CtbLog2SizeY), the variable value being CtbLog 2SizeY.
 16. Theapparatus of claim 9, wherein the coded information is in a sequenceparameter set header for the coded video sequence.
 17. A non-transitorycomputer-readable storage medium storing a program executable by atleast one processor to perform: receiving coded information of picturesin a coded video sequence, the coded information including a coding treeunit (CTU) size information that indicates a CTU size selected for thepictures from three CTU sizes; determining, based on at least one bitcorresponding to the CTU size information, the selected CTU size; andreconstructing samples in the pictures based on the selected CTU size,wherein the selected CTU size is determined as a first CTU size of thethree CTU sizes based on a first bit of the at least one bitcorresponding to the CTU size information being a first value, theselected CTU size is determined as one of a second CTU size and a thirdCTU size of the three CTU sizes based on the first bit being a secondvalue and a second bit of the at least one bit corresponding to the CTUsize information, and the at least one bit includes the second bit basedon the first bit being the second value.
 18. The non-transitorycomputer-readable storage medium of claim 17, wherein the three CTUsizes are 32, 64, and 128, and the selected CTU size is 32, 64, or 128indicating each of the pictures has 32×32, 64×64, or 128×128 lumasamples, respectively.
 19. The non-transitory computer-readable storagemedium of claim 18, wherein the program is to perform: determining,based on the CTU size information encoded using a truncated unarycoding, a coded value from the at least one bit in the codedinformation, a maximum number of bits in the at least one bit being 2,the coded value being 0 when the at least one bit is 0, the coded valuebeing 1 when the at least one bit is 10, and the coded value being 2when the at least one bit is
 11. 20. The non-transitorycomputer-readable storage medium of claim 19, wherein the determiningthe selected CTU size comprises determining that the selected CTU sizeis 128, 64, or 32 in a case that the coded value is 0, 1, or 2,respectively.